> Firefox is the only that has their own rendering engine and is cross platform.

Interestingly safaris rendering engine is open source and cross platform, but the browser is not. Lots of linux-focused browsers (konquerer, gnome web, surf) and most embedded browsers (nintendo ds & switch, playstation) use webkit. Also some user interfaces (like WebOS, which is running all of LG's TVs and smart refrigerators) use webkit as their renderer.